锁分类

悲观锁

• 不支持并发

  乐观锁

  

• 通过版本号来控制，支持并发

  表锁

  不会发生死锁

  行锁

  会发生死锁

  读锁

  也叫共享锁，会发生死锁

  写锁

  也叫独占锁，会发生死锁

读写锁ReentrantReadWriteLock

package com.daijunyi.lock;
import java.util.HashMap;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantReadWriteLock;
class Cache{
    private volatile HashMap<String,Object> map = new HashMap<>();
    //读写锁
    private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
    public void put(String key,String value){
        rwLock.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName()+"开始做存储操作");
            TimeUnit.SECONDS.sleep(new Random().nextInt(5));
            map.put(key,value);
            System.out.println(Thread.currentThread().getName()+"+++存储完成");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            rwLock.writeLock().unlock();
        }
    }
    public Object get(String key){
        rwLock.readLock().lock();
        Object value = null;
        try {
            System.out.println(Thread.currentThread().getName()+"---读操作");
            TimeUnit.SECONDS.sleep(new Random().nextInt(4));
            value = map.get(key);
            System.out.println(Thread.currentThread().getName()+"读操作完成");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            rwLock.readLock().unlock();
        }
        return value;
    }
}
//读写锁
public class ReadWriteDemo {
    public static void main(String[] args) {
        Cache cache = new Cache();
        //写操作
        for (int i=0;i<4;i++){
            final String num = String.valueOf(i);
            new Thread(()->{
                cache.put(num,num);
            },num).start();
        }
        //读操作
        for (int i=0;i<4;i++){
            final String num = String.valueOf(i);
            new Thread(()->{
                Object o = cache.get(num);
                System.out.println("读操作"+o);
            },num).start();
        }
    }
}

运行结果

/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/bin/java -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/tools.jar:/Users/djy/WorkFile/learn/juc/picker/target/classes com.daijunyi.lock.ReadWriteDemo
0开始做存储操作
0+++存储完成
1开始做存储操作
1+++存储完成
2开始做存储操作
2+++存储完成
3开始做存储操作
3+++存储完成
0---读操作
1---读操作
2---读操作
3---读操作
2读操作完成
读操作2
3读操作完成
读操作3
0读操作完成
读操作0
1读操作完成
读操作1
Process finished with exit code 0